This invention relates to rotating machines and more particularly to monitoring of the vibration of such machines.
In the realm of vibration monitoring of a rotating machine such as a turbine generator, it is sometimes desirable to know the amplitude of a signal received from a vibration sensing probe minus the fundamental frequency associated with the running speed of the rotating machinery shaft. This is known as the Not 1X waveform. Variations in the amplitude of this waveform could signal problems with bearings, rotors such as misalignment, cracks or mechanical looseness, and or fluids of the rotating machine.
The present invention describes a method implemented in conjunction with a sampled data system to compute the amplitude of the Not 1X waveform and provide the result in either peak to peak amplitude, peak amplitude, absolute average, or root mean square (RMS).
The present invention is a method for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The method stores a predetermined percentage of samples of the waveform obtained at a predetermined sampling rate in a bin of data in a memory. The method further associates a speed of the shaft with each of the stored samples. The method also further determines the center frequency of a bandstop filter through which the samples stored in the memory data bin are passed by averaging the speed of the shaft associated with each of the stored samples. The method further accumulates a predetermined number of the stored samples starting with the first of the stored samples; and uses the accumulated stored samples to provide a data point that is free of any residual bias in the samples.
The present is also a method for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The method stores a predetermined percentage of samples of the waveform obtained at a predetermined sampling rate in a bin of data in a memory. The method also associates a speed of the shaft with each of the stored samples. The method also further determines the center frequency of a bandstop filter through which the samples stored in the memory data bin are passed by averaging the speed of the shaft associated with each of the stored samples. The method further accumulates a predetermined number of the stored samples starting with the first of the stored samples; and calculates the average of the accumulated stored samples.
The present invention is further a method for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The method samples the waveform at a predetermined sampling rate and stores a predetermined percentage of the samples in a bin of data in a memory. The method also associates a speed of the shaft with each of the stored samples and passes the samples stored in the memory data bin through a bandstop filter. The method also further determines the center frequency of the filter by averaging the speed of the shaft associated with each of the stored samples. The method further accumulates a predetermined number of the stored samples starting with the first of the stored samples; and calculates the average of the accumulated stored samples.
The present invention is further also a method for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The method stores a predetermined percentage of samples of the waveform obtained at a predetermined sampling rate in a bin of data in a memory; and associates a speed of the shaft with each of the stored samples. The method also determines the center frequency of a bandstop filter through which the samples stored in the memory data bin are passed by averaging the speed of the shaft associated with each of the stored samples. The method further also accumulates in an accumulator a predetermined number of the stored samples starting with the first of the stored samples; and uses the accumulated stored samples to provide a data point that is free of any residual bias in the samples. The method further stores the accumulated value when the accumulated value is close to overflow; and sets the accumulator to zero.
The present is a system for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The system has:
a) means for storing a predetermined percentage of samples of the waveform obtained at a predetermined sampling rate in a bin of data in a memory;
b) means for associating a speed of the shaft with each of the stored samples;
c) means for determining the center frequency of a bandstop filter through which the samples stored in the memory data bin are passed by averaging the speed of the shaft associated with each of the stored samples;
d) means for accumulating a predetermined number of the stored samples starting with the first of the stored samples; and
e) means for using the accumulated stored samples to provide a data point that is free of any residual bias in the samples.
The present invention is also a system for calculating the amplitude of a waveform associated with a rotating machine shaft after removing the fundamental frequency thereof. The system has:
a) a bin of data in a memory to store a predetermined percentage of samples of the waveform obtained at a predetermined sampling rate; and
b) a computing device operative to:
(i) associate a speed of the shaft with each of the stored samples;
(ii) determine the center frequency of a bandstop filter through which the samples stored in the memory data bin are passed by averaging the speed of the shaft associated with each of the stored samples;
(iii) accumulate a predetermined number of the stored samples starting with the first of the stored samples; and
(iv) use the accumulated stored samples to provide a data point that is free of any residual bias in the samples.